Quilting is a special art in the general field of sewing in which patterns are stitched through a plurality of layers of material over a two-dimensional area of the material. The multiple layers of material normally include at least three layers, one a woven primary or facing sheet having a decorative finished quality, one a usually woven backing sheet that may or may not be of a finished quality, and one or more internal layers of thick filler material, usually of randomly oriented fibers. The stitched patterns maintain the physical relationship of the layers of material to each other as well as provide ornamental qualities. Quilting is performed on the customary quilts or comforters and on the covers of mattresses, for example. In the stitching of quilts for these two applications, two different approaches are typically used. Both approaches use stitches that employ both a top and a bottom thread.
Single needle quilters of the type illustrated and described in U.S. Pat. Nos. 5,640,916 and 5,685,250, hereby expressly incorporated by reference herein, and those patents cited and otherwise referred to therein are customarily used or the stitching of comforters and other preformed rectangular panels. Such single needle quilters typically use a pair of cooperating a lock stitch sewing heads, one carrying a needle drive that is typically positioned above the fabric and one carrying a bobbin that is opposite the fabric from the needle, with both heads being mechanically linked to move together in two dimensions, relative to the panel, parallel to the plane of the panel. A common arrangement of this type of quilting apparatus is to support the panel of fabric on a longitudinally moveable shuttle with the sewing heads moveable transversely of the panel to provide two-dimensional stitching capability of the pattern on the panel.
Multiple needle quilters of the type illustrated in U.S. Pat. No. 5,154,130 are customarily used for the stitching of mattress covers, which are commonly formed from multilayered web-fed material. Such multi-needle quilters typically use an array of cooperating a double chain stitch sewing elements, one element being a needle that is typically positioned above the material and one element being a looper that is opposite the material from the needle, with the entire arrays of both elements being mechanically linked together to move in unison in two dimensions, relative to the material, parallel to the plane of the material in paths that corresponds to identical patterns of a pattern array. The needles and loopers also operate in unison so that the sets of elements simultaneously form identical series of stitches. A common arrangement of this type of quilting apparatus is to support the panel of multilayered material and feed the material from a web longitudinally relative to the sewing element array and in coordination with the motion and operation of the sewing elements. The sewing element array may be shiftable transversely of the web to provide two-dimensional stitching capability of the pattern on a panel length of the web. Alternatively, the array is stationary and rollers that support the web shift transversely relative to the array. Some multi-needle quilters of this type have longitudinally bi-directional web feeding capability which, when synchronized with the transverse shifting of the web or the sewing elements, provides for 360.degree. pattern sewing capability.
The single needle quilters are regarded as preferable for the sewing of a wider range of patterns and particularly more highly decorative patterns. In addition, in single needle quilters, the lock stitch is commonly used. Lock stitch machines, with their needle and bobbin arrangement, have been made somewhat able to tolerate or avoid needle deflection problems that can result in a missing of stitches when a needle is deflected. Needle deflection is more of a problem when quilting thick materials and complex patterns that involve many directional changes in the sewing path, particularly where higher sewing speeds are used. The lock stitch also provides equally aesthetically acceptable stitching on both sides of the fabric.
The multi-needle quilters are regarded as preferable for sewing mattress covers. With mattress covers, the less attractive looper side stitch may be confined to the inside of the mattress cover on the backing layer of material that is not visible to the observer. Further, the double chain stitch heads of the multi-needle quilters apply a looper side thread from an external spool, which can accommodate a substantially larger thread supply than can the bobbin of a lock stitch machine. As a result, the lock stitch machine can be run longer before the need arises to replenish the bottom thread supplies. The bobbins of the lock stitch machines require frequent changing, particularly with thick multilayered materials such as mattress covers which require more thread per stitch. A drawback to the use of double chain stitch machines has been the greater likelihood for stitches to be missed as a result of needle deflection. This is in part because a double chain stitch requires the looper on one side of the material to enter a thread loop in close proximity to the needle that has passed through the material from the other side, which needle itself must pass through a thread loop presented by the looper. Misalignment of the needle and looper due to deflection of the needle can result in the missing of stitches which, in the formation of more highly decorative patterns, is undesirable for not only aesthetic reasons but because it can result in an unraveling of the stitched pattern. Attempts at high speed sewing on mattress covers, where the material is generally very thick and the outer or ticking layer of fabric may be heavy and even of an upholstery-like nature, produce unavoidable needle deflection.
With the increased use of computerized pattern control and the resulting ability to provide a wider variety of quilted patterns, particularly patterns of a high ornamental quality, there has been an increasing demand for an ability to sew more, more complex and larger patterns onto the covers of mattresses. To this end, equipment of the prior art such as discussed above has had limitations. Accordingly, there remains a need for a capability to stitch more highly ornamental and complex patterns onto mattress covers at high speed.